High load formulations and methods for providing prolonged local anesthesia

ABSTRACT

A formulation for inducing sustained local anesthesia in a patient comprising a substrate comprising a high load of local anesthetic by weight and an effective amount of a biocompatible, controlled release material to obtain a. reversible nerve blockade or anesthesia effect when implanted or injected in a patient, and a non-toxic glucocorticosteroid agent effective to prolong the duration of the local anesthesia for a time period longer than that obtainable from the substrate without the glucocorticosteroid agent.

This application is a continuation application of U.S. Ser. No.08/714,782, filed Sep. 16, 1996, now U.S. Pat. No. 5,922,340, which is acontinuation-in-part application of U.S. Ser. No. 08/432,402, filed May1, 1995, now U.S. Pat. No. 5,700,485, which is a continuation-in-part ofU.S. Ser. No. 08/119,958, filed Sep. 10, 1993, now U.S. Pat. No.5,618,563, which is a continuation-in-part of Ser. No. 07/943,287, filedSep. 10, 1992, now abandoned, the entire disclosures of which are herebyincorporated by reference.

The U.S. Government may have rights in this invention pursuant toNational Institutes of Health Grant No. GM-1 5904 to Harvard AnesthesiaResearch and Teaching Center to C. Berde, and Grant No. CA 5257 to R.Langer.

FIELD OF THE INVENTION

The present invention is related to biocompatible controlled releaseformulations including formulations comprising surprisingly high loadsof local anesthetic, for providing local anesthesia of sustainedduration, as well as to methods for providing the same.

BACKGROUND OF THE INVENTION

While compounds utilized as general anesthetics reduce pain by producinga loss of consciousness, local anesthetics act via a loss of sensationin the localized area of administration in the body. The mechanism bywhich local anesthetics induce their effect, while not having beendetermined definitively, is generally thought to be based upon theability to locally interfere with the initiation and transmission of anerve impulse, e.g., interfering with the initiation and/or propagationof a depolarization wave in a localized area of nerve tissue. Theactions of local anesthetics are general, and any tissue where nerveconduction, e.g., cell membrane depolarization occurs can be affected bythese drugs. Thus, nervous tissue mediating both sensory and motorfunctions can be similarly affected by local anesthetics.

The duration of action of a local anesthetic is proportional to the timeduring which it is in actual contact with the nervous tissues.Consequently, previous attempts to prolong the duration of localanesthesia have focused on. procedures or formulations that maintainlocalization of the drug at the nerve. For example, epinephrine is artknown to briefly prolong the action of local anesthetics by inducingvasoconstriction adjacent to the site of injection. However, theduration of prolongation provided by epinephrine is on the order ofabout an hour, at best, in a highly vascularized tissue. This strategyis also severely limited by the risk of gangrene due to prolongedimpairment of blood flow to local tissues.

The art has also attempted to prolong the duration of local anesthesiaby providing more lipid-soluble compounds for use as long-actinganesthetics, i.e., local anesthetics that have a prolonged localanesthetic affect, but even these compounds provide a relatively limitedduration of activity. For example, local anesthetics with a relativelyshort duration of action include, e.g., procaine with a duration ofranging from about 20-45 minutes, local anesthetics with an intermediateduration of action, e.g., lidocaine or mepivacaine, with a duration ofaction ranging from about 60-120 minutes and local anesthetics with along duration of action, e.g., bupivacaine or etidocaine, with aduration ranging, under the most favorable circumstances, from about 400to 450 minutes. However, this strategy for prolonging local anesthesiais limited by the possibility of local and systemic toxicity fromexcessive drug levels.

In fact, all local anesthetics are toxic, i.e., potentially toxic, andtherefore it is of great importance that the choice of drug,concentration, rate and site of administration, as well as otherfactors, be considered in their use. On the other hand, as the precedingdiscussion makes clear, a local anesthetic must remain at the site longenough to allow sufficient time for the localized pain to subside.

Other pharmacological methods for prolonging local anesthesia have alsobeen tried. European Patent Application No. 93922174.3 by Children'sMedical, Center Corporation, discloses biodegradable synthetic polymersreleasing local anesthetic over prolonged periods of time, as measuredin vitro. Dexamethasone was included in the described formulation simplyin order to avoid inflammation due to the polymer that was employed,however, the formulations described therein were of relatively lowloading, e.g., microspheres with about 20% loading were exemplified, andit was taught by that publication that the duration of local anestheticaction was dependent upon the nature of the controlled release polymersdescribed therein.

Other formulations directed to injectable microparticles and/ormicrocapsules, etc. are known. For example, U.S. Pat. No. 5,061,492related to prolonged release microcapsules of a water-soluble drug in abiodegradable polymer matrix which is composed of a copolymer ofglycolic acid and a lactic acid. The microcapsules are prepared as aninjectable preparation in a pharmaceutically acceptable vehicle. Theparticles of water soluble drug are retained in a drug-retainingsubstance dispersed in a matrix of the lactic/glycolic acid copolymer ina ratio of 100/1 to 50/50 and an average molecular weight of5,000-200,000. The injectable preparation is made by preparing awater-in-oil emulsion of aqueous layer of drug and drug retainingsubstance and an oil layer of the polymer, thickening and thenwater-drying. In addition, controlled release microparticles containingglucocorticoid agents are described, for example, by Tice et al. in U.S.Pat. No. 4,530,840.

In order to provide local anesthesia for extended periods, i.e., formore than about six hours, clinicians currently use local anestheticagents administered through a catheter or syringe to a site whereanesthesia is to be induced. Thus, prolonged local anesthesia, where theanesthesia is to be maintained over a period of greater than about 6hours, has heretofore required that local anesthetic be administeredeither as a bolus or through an indwelling catheter connected to aninfusion pump.

Thus, it has not heretofore been known to provide controlled releaseformulations with a relatively high loading of local anesthetic at alevel that is substantially above 20% by weight, that is able to provideboth a controlled release of local anesthetic and a substantiallyprolonged local anesthesia. It has also not heretofore been known tocombine a formulation with a relatively high loading of a localanesthetic, e.g., substantially above 20% by weight, with aglucocorticosteroid agent in either immediate release or controlledrelease form, for providing prolonged local anesthesia that is achievedwithout a significant modification of the in vitro kinetics of localanesthetic release from the formulation.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide acontrolled release dosage form for prolonged treatment of localizedareas in humans and animals. More particularly, it is an object of theinvention to provide formulations and methods for delivering a high loadof local anesthetic in a biocompatible, controlled release form whichprovides a prolonged local anesthesia.

It is a further object of the present invention to provide a method forprolonging the effect of a local anesthetic agent at a desired site oftreatment which is safe and effective, particularly for the control ofpost-operative pain.

It is a still further object to prolong the duration of the localanesthesia by administering a glucocorticosteroid agent (also referredto herein as glucocorticoid agents) in combination with a high loadingof local anesthetic formulation or separately from the local anestheticformulation, before, during or after the infiltration, injection orimplantation of the compositions according to the invention.

SUMMARY OF THE INVENTION

In accordance with the above-mentioned objects and others, the inventionis related to controlled release formulations for the prolongedadministration of a high load, by weight percent, of a local anestheticagent. In a preferred aspect, the high load controlled release localanesthetic is administered in combination with a glucocorticosteroidagent that is effective to prolong the duration of the local anestheticeffect, in vivo, for a time period greater than that possible by the useof the local anesthetic in controlled release form alone. Methods forthe manufacture thereof are also disclosed. The controlled releaseformulation can be formed into slabs, pellets, microparticles, e.g.,microspheres or microcapsules, spheroids and pastes suitable forinsertion, implantation, injection, infiltration or topical application.Preferably, the formulation is in a form suitable for suspension inisotonic saline, physiological buffer and/or any other art-known vehicleacceptable for injection and/or infiltration into a patient.

The invention further provides methods for inducing localized anesthesiaby implanting, inserting, infiltrating or injecting a controlled releaseformulation, e.g., in the form of injectable microspheres loaded with arelatively high loading of local anesthetic in sustained release form,into a site at or adjacent to a nerve or nerves innervating a bodyregion to provide local anesthesia. Thus, the controlled releaseformulation according to the invention is injected, infiltrated,implanted or applied (e.g., topically) at a site in a patient where thelocal anesthetic agent is to be released.

Further aspects of the invention are directed to a method of treating apatient in need of a surgical procedure, comprising placing a localanesthetic in controlled release form adjacent to and/or in proximity toa nerve or nerves at the surgical site, and simultaneously and/orsubsequently administering the aforementioned glucocorticosteroid agentto substantially the same site, to attain a prolongation of localanesthesia otherwise unattainable with the use of the local anestheticalone.

The invention also provides for a unit dosage of the controlled releaseformulation comprising, in a container, a sufficient amount of theformulation to induce local anesthesia in at least one patient. In oneembodiment, the unit dosages are sterile and lyophilized. Alternatively,the unit dosages are sterile and prepared as a suspension in a solutionacceptable for injection into a patient.

The invention is further directed, in part, to novel formulations forproviding local anesthesia, comprising a pharmaceutically-acceptablelocal anesthetic agent in controlled release form, said formulationbeing capable of being placed adjacent to and/or in proximity to a nervewhich is to be anesthetized, and an effective amount of aglucocorticosteroid agent capable of prolonging the localized anestheticeffect provided by the local anesthetic in controlled release form. Theglucocorticosteroid agent may be incorporated with the local anesthetic,or alternatively, at least part of the dose of the glucocorticosteroidagent may be administered separately but in proximity to the samelocation as the local anesthetic. At least a part of such a separatedose may be administered later in time than the local anesthetic, toprovide additional prolongation of the extent and/or duration of thelocal anesthetic effect.

A portion of the local anesthetic can be administered to the desiredsite in immediate release form as long as a portion of the localanesthetic is also administered in controlled release form. In furtherembodiments, the invention is directed to a suspension comprising aplurality of controlled release, microparticles, e.g., microspheresand/or microcapsules comprising a local anesthetic agent, together withat least a portion of the glucocorticosteroid agent incorporated in thecontrolled release microparticles, or optionally, theglucocorticosteroid dissolved or suspended in a pharmacologicallyacceptable vehicle. The vehicle may be the same as that in which themicroparticles are suspended, or may comprise a formulation for separateadministration in controlled release and/or immediate release form inwhich the microparticles are suspended. The vehicle is, for example,suitable for administering the microparticles by injection. Optionally,at least a portion of the local anesthetic is incorporated into acontrolled release formulation including a glucocorticosteroid agentcoated on the surface thereof.

In yet additional embodiments of the invention, the formulationcomprises a local anesthetic core and a glucocorticosteroid agentpresent in the core in an amount effective to prolong the effect of thelocal anesthetic in an environment of use, and a coating on the corethat is effective to provide a slow release of the local anesthetic andglucocorticosteroid agent in an environment of use.

The glucocorticosteroid agent may also be systemically administered byinjection, instillation, infiltration, oral dosing, topically or by anyother art known method to obtain the desired prolongation of effect.Systemic administration (e.g., oral or intravenous) will require ahigher total dose of a glucocorticosteroid agent than will localadministration in proximity to the site of local anestheticadministration.

The controlled release local anesthetic dosage form may be injected,with or without a glucocorticosteroid agent, at the site where theanesthetic is to be released. This can be prior to surgery, at the timeof surgery, or following removal (discontinuation) or reversal of asystemic anesthetic.

Examples demonstrate prolongation of the duration of local anesthesiawith the greater prolongation being provided by the combination of alocal anesthetic with a glucocorticosteroid agent.

Accordingly, the invention provides formulations with a high loading oflocal anesthetic by weight, relative to that heretofore available, toprovide a prolonged localized local anesthesia. Surprisingly andunexpectedly, the formulations and methods according to the inventionhaving relatively high drug loading, with relatively low proportions ofcontrolled release carrier, allow for the sustained release of a localanesthetic agent and for a prolonged local anesthesia.

In addition, the administration of an effective amount -of at least onepharmaceutically acceptable glucocorticosteroid agent or agents, inconjunction with a local anesthetic agent in controlled release form,unexpectedly increases the duration of local anesthesia when both typesof agent are administered at a site to be anesthetized, or to a sitethat has previously been anesthetized, in a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of percent cumulative release of radio labeledbupivacaine versus time (days), in vitro, comparing microspherescontaining either radiolabeled dexamethasone/unradiolabeled bupaivcainecontaining microspheres and with radiolabeled bupivacaine/unradiolabeleddexamethasone microspheres.

FIG. 2 is a graph of the duration of sensory latency (hours) versesbupivacaine dose, in animals treated with microspheres containingbupivacaine 75% (w/w) and 0.05% dexamethasone prepared from 100polylactic acid (“PLA”; square), copolymer of lactic and glycolic acid(“PLGA”) 65:35 (circle), and PLGA 75:25 (triangle) loaded withbupivacaine and dexamethasone, administered at doses of 50 to 450 mg ofbupivacaine/Kg rat. Duration was defined as the mean duration of timefor which the for which the latency of a group of 5 rats was greaterthan or equal to 7 seconds. Error bars indicate standard errors.

FIG. 3A is a graph of the duration of latency versus time (hours),determined by sensory testing using the modified hot plate test for 75%bupivacaine loaded PLGA 65:35 containing 0.05%, 0.005%, and 0.0%dexamethasone. Error bars indicate standard errors.

FIG. 3B is a graph of the duration of latency versus time (hours),determined by by motor testing (FIG. 3b) for 75% bupivacaine loaded PLGA65:35 containing 0.05%, 0.005%, and 0% dexamethasone. Error barsindicate standard errors.

FIG. 4A is a graph comparing the duration of latency (secs) versus time(hours) after injection, determined using the modified hot plate testfor 100 PLA microspheres loaded with 75% bupivacaine which contained0.05% dexamethasone (circles) with corresponding microspheres which didnot contain dexamethasone (squares). Error bars indicate standarderrors.

FIG. 4B is a graph comparing the duration of latency (secs) versus time(hours) after injection, determined using the modified hot plate testfor PLGA 75:25 microspheres loaded with 75% bupivacaine which contained0.05% dexamethasone (squares) with corresponding microspheres which didnot contain dexamethasone (circles). Error bars indicate standarderrors.

FIG. 4C is a graph comparing the duration of latency (secs) versus time(hours) after injection, determined using the modified hot plate testfor 65:35 PLGA microspheres loaded with 75% bupivacaine which contained0.05% dexamethasone (open squares) with corresponding microspheres whichdo not contain dexamethasone (closed circles). Error bars indicatestandard errors.

FIG. 4D is a graph comparing the duration of latency (secs) versus time(hours) after injection, determined using the modified hot plate testfor 50:50 PLGA microspheres loaded with 75% bupivacaine which contained0.05% dexamethasone (squares) with corresponding microspheres which donot contain dexamethasone (circles). Error bars indicate standarderrors.

FIGS. 5A is a graph of the duration of sensory block in hours afterinjection of bupivacaine loaded microspheres (circles), bupivacaineloaded microspheres with dexamethasone in the injection fluid (squares),and bupivacaine loaded microspheres with betamethasone in the injectionfluid (triangles).

FIG. 5B is a graph of the duration of motor block in hours afterinjection of bupivacaine loaded microspheres (triangles), bupivacaineloaded microspheres with dexamethasone in the injection fluid (squares),and bupivacaine loaded microspheres with betamethasone in the injectionfluid (circles).

FIG. 6 is a graph of sensory block over time after injection (hours) inrats of PLGA 65:35 microspheres containing bupivacaine and with one offour glucocorticoids in the injection fluid: betamethasone (0.8 mg/kg),dexamethasone (0.14 mg/kg), methylprednisolone (0.1 mg/kg), andhydrocortisone (1.25 mg/kg) in the injection fluid.

FIG. 7 is graph of the percent cumulative release over time (days) formicrospheres containing 75%, bupivacaine, by weight, prepared from PLA100 (squares), PLGA 75.25 (closed circles), PLGA 65:35 triangles andPLGA 50:50 (circles).

DETAILED DESCRIPTION

While the mechanism for glucocorticoid-induced prolongation of theduration of local anesthesia is not fully understood, it has beendetermined that the prolongation of local anesthesia provided by theformulations of the present invention cannot be predicted based entirelyon the controlled release properties of the carrier used in theformulation, because of the relatively low proportions, e.g., about 25%,(w/w) of the carrier that is preferably employed, e.g., in microspherescomprising about 75% bupivacaine (w/w).

Further, it has been determined that the prolongation of the duration oflocal anesthesia by the use of a glucocorticosteroid agent cannot bepredicted based on the in vitro release (dissolution) of the localanesthetic in controlled release form because the inclusion of theglucocorticosteroid agent within the controlled release formulations ofthe invention does not substantially alter or prolong the in vitrodissolution rate of the local anesthetic agent from the formulation.Instead, the same formulation when administered in vivo provides asignificant increase in the time period of local anesthesia at the siteof administration.

The glucocorticosteroid agents disclosed herein can be administeredprior to, along with, or after injection of the local anesthetic agentin controlled release form, in each case with a substantial prolongationof local anesthesia, in vivo.

The glucocorticosteroid agent can be compounded in the same controlledrelease formulation as a local anesthetic agent, in a separatecontrolled release formulation, e.g., different injectable microspheres,or in a non-controlled release formulation.

In those embodiments of the invention directed to formulations where theglucocorticosteroid agent is included, the glucocorticosteroid agent maybe included in controlled release form or in immediate release form. Theglucocorticosteroid agent may be incorporated into the controlledrelease matrix along with the local anesthetic; incorporated into acontrolled release coating on a sustained release device or formulation;or incorporated as an immediate release layer coating the localanesthetic formulation. On the other hand, the glucocorticosteroid agentmay be incorporated into a pharmaceutically acceptable vehicle or mediumsuitable for topical administration, either in sustained release form orin immediate release form.

The controlled release formulations and methods of the invention may beused in conjunction with any implantable, insertable or injectablesystem known in the art, including but not limited to microspheres,microcapsules, gels, pastes, implantable rods, pellets, plates orfibers, and the like (generically referred to as “substrates”).

As used herein, the term “local anesthetic agent” means any drug whichprovides local numbness and/or analgesia. Examples of local anestheticagents which can be used include bupivacaine, ropivacaine, dibucaine,procaine, chloroprocaine, prilocaine, mepivacaine, etidocaine,tetracaine, lidocaine, and xylocaine, and mixtures thereof. The localanesthetic can be in the form of a salt, for example, the hydrochloride,bromide, acetate, citrate, carbonate or sulfate. More preferably, thelocal anesthetic agent is in the form of a free base. Preferred localanesthetic agents include, e.g., bupivacaine. For example, forbupivacaine, the free base provides a slower initial release and avoidsan early “dumping” of the local anesthetic at the injection site. Otherlocal anesthetics may act differently. Local anesthetic agents typicallyadministered systematically may also be used in those cases where themeans of administration results only in a local effect, rather thansystemic. The term “local anesthesia” includes the conditions of, e.g.,local numbness and/or analgesic and/or inhibitory. effects on motorfunction induced, simply by way of example, by a local anesthetic asdefined above.

The term “local anesthetic” may also encompass, pursuant to thedefinitions provided herein, a drug of a different class than thosetraditionally associated with local anesthetic properties, including butnot limited to morphine, fentanyl, and agents which, for example, canprovide regional blockade of nociceptive pathways (afferent and/orefferent). The formulations according to the invention preferablyprovide high load formulations of controlled release local anestheticagent.

The term, “local anesthesia” includes the condition of, e.g., a localnumbness and/or analgesia, and/or inhibitory effects on sensory andmotor function, induced, simply by way of example, by a local anestheticas defined above.

The term, “controlled release” generally refers to compositions, e.g.,pharmaceutically acceptable carriers, for controlling the release of anactive agent or drug incorporated therein, typically by slowing therelease of the active agent or drug in order to prevent immediaterelease. Such controlled release compositions and/or carriers are usedherein to prolong or sustain the release of an active agent or drugincorporated, e.g., a local anesthetic and/or a glucocorticoid agent.Thus, the terms “controlled release” and “sustained release” aregenerally used interchangeably throughout this document unless otherwiseindicated.

The phrase, “high load” or “high loading” as used herein indicates thatthe local anesthetic agent makes up substantially greater than 20% ofthe formulation, by weight. Thus, simply by way of example, a high loadlocal anesthetic formulation comprises from about 30% loading to about90% loading of local anesthetic relative to the total weight of theformulation, by weight. In a preferred aspect, a high load formulationcomprises from about 60% to about 85% local anesthetic by weight, oreven from about 70% to about 80% local anesthetic by weight. Mostpreferably, a high load formulation comprises about 75%, by weight, oflocal anesthetic agent, relative to the total weight of the formulation.

As used herein, the term “patient” broadly refers to any animal that isto be treated with the compositions and by the methods herein disclosed.The disclosed local anesthetic dosage form can provide localizedanesthesia to any animal, e.g., any vertebrate, which it is desired toso anesthetize. In particular, the disclosed methods and compositionswill find use in veterinary practice and animal husbandry for, e.g.,birds and mammals, wherever prolonged local anesthesia is convenient ordesirable. In a preferred embodiment, the term includes humans in needof or desiring prolonged local anesthesia.

The methods and formulations according to the invention may be applied,e.g., topically. Thus, any pharmaceutically acceptable formulationsuitable for topical administration, e.g., to the skin or mucosalsurfaces may be employed for administration of a local anesthetic and/ora glucocorticoid agent according to the invention, either as a singleformulation or in separate formulations for inducing topical localanesthesia.

For internal administration, any formulation suitable for localimplantation, infiltration or injection in proximity to a nerve that isable to provide a controlled release of a local anesthetic agent may beemployed to provide for prolonged local anesthesia as needed. Slowrelease formulations or carriers known in the art include, e.g.,emulsions, liposomes and liposome-like preparations, as well asspecially coated pellets, polymer formulations or matrices for surgicalinsertion or as controlled release microparticles or microspheres forimplantation, infiltration, insertion or injection, wherein the slowrelease of the active medicament is brought about through controlleddiffusion out of the e.g., a carrier material and/or matrix and/orthrough selective breakdown of the coating of the preparation orselective breakdown of a polymer matrix.

The carrier material should be pharmaceutically acceptable, i.e.,biocompatible and free from undesirable impurities. In the case ofpolymeric materials, biocompatability is enhanced using standardtechniques designed to , remove undesirable impurities, e.g., byrecrystallization of either the monomers forming the polymer and/or thepolymer using standard techniques designed to remove undesirableimpurities. Optionally, the biocompatible carrier may be biodegradableor non-biodegradable.

Simply by way of example, the controlled release carrier or materialincludes suitable biocompatible polymers. The polymeric material maycomprise a polylactide, a polyglycolide, a poly(lactide-co-glycolide), apolyanhydride, a poblyorthoester, polycaprolactones, polyphosphazenes,polysaccharides, proteinaceous polymers, soluble derivatives ofpolysaccharides, soluble derivatives of proteinaceous polymers,polypeptides, polyesters, and polyorthoesters. The polysaccharides maybe poly-1,4-glucans, e.g., starch glycogen, amylose, amylopectin, andmixtures thereof. The hydrophilic or hydrophobic polymer may be awater-soluble derivative of a poly-1,4-glucan, including hydrolyzedamylopectin, hydroxyalkyl derivatives of hydrolyzed amylopectin such ashydroxyethyl starch ES), hydroxyethyl amylose, dialdehyde starch, andthe like. Preferred controlled release materials which are useful in theformulations of the invention include the polyanhydrides, co-polymers oflactic acid and glycolic acid wherein the weight ratio of lactic acid toglycolic acid is no more than 4:1 (i.e., 80% or less lactic acid to 20%or more glycolic acid by weight), and polyorthoesters containing acatalyst or degradation enhancing compound, for example, containing atleast 1% by weight anhydride catalyst such as maleic anhydride. Otheruseful polymers include protein polymers such as gelatin and fibrin andpolysaccharides such as hyaluronic acid. Since polylactic acid takes atleast one year to degrade in vivo, this polymer should be utilized byitself only in circumstances where such a degradation rate is desirableor acceptable.

The polymeric material may be prepared by any method known to thoseskilled in the art. For example, where the polymeric material iscomprised of a copolymer of lactic and glycolic acid, this copolymer maybe prepared by the procedure set forth in U.S. Pat. No. 4,293,539(Ludwig, et al.), hereby incorporated by reference. Basically, thereinthe copolymers are prepared by condensation of lactic acid and glycolicacid in the presence of a readily removable polymerization catalyst(e.g., a strong acid ion-exchange resin such as Dowex HCR-W2-H). Theamount of catalyst is not critical to the polymerization, but typicallyis from about 0.01 to about 20 parts by weight relative to the totalweight of combined lactic acid and glycolic acid. The polymerizationreaction may be conducted without solvents at a temperature from about100° C. to about 250° C. for about 48 to about 96 hours, preferablyunder a reduced pressure to facilitate removal of water and by-products.The copolymer is then recovered by filtering the molten reaction mixtureto remove substantially all of the catalyst, or by cooling and thendissolving the reaction mixture in an organic solvent such asdichloromethane or acetone and then filtering to remove the catalyst.

Polyanhydrides may be prepared in accordance with the methods set forthin U.S. Pat. No. 4,757,128, hereby incorporated by reference. Forexample, polyanhydrides may be synthesized by melt polycondensation ofhighly pure dicarboxylic acid monomers converted to the mixed anhydrideby reflux in acetic anhydride, isolation and purification of theisolated prepolymers by recrystallization, and melt polymerization underlow pressure (10⁻⁴ mm) with a dry ice/acetone trap at a temperaturebetween 140°-250° C., for 10-300 minutes. High molecular weightpolyanhydrides are obtained by inclusion of a catalyst which increasesthe rate of anhydride interchain exchange, for example, alkaline earthmetal oxides such as CaO, BaO and CaCo₃. Polyorthoester polymers may beprepared, e.g., as set forth in U.S. Pat. No. 4,070,347, herebyincorporated by reference.

Various commercially available poly (lactide-co-glycolide) materials(PLGA) may be used in the preparation of the formulations, e.g.,microspheres of the present invention. For example,poly(d,l-lactic-co-glycolic acid) are commercially available. Apreferred commercially available product is a 50:50 poly (D,L) lacticco-glycolic acid. This product has a mole percent composition of 50%lactide and 50% glycolide. Other suitable commercially availableproducts are (lactide: glycolide) 65:35 DL, 75:25 DL, 85:15 DL andpoly(d,l-lactic acid) (d,l-PLA). For example,poly(lactide-co-glycolides) are commercially available from BoerhingerIngelheim (Germany) under its ResomerC mark, e.g., PLGA 50:50 (ResomerRG 502), PLGA 75:25 (Resomer RG 752) and d,l-PLA (resomer RG 206), andfrom Birmingham Polymers (Birmingham, Alabama). These copolymers areavailable in a wide range of molecular weights and ratios of lactic toglycolic acid.

Pharmaceutically acceptable polyanhydrides which are useful in thepresent invention have a water-labile anhydride linkage. The rate ofdrug release can be controlled by the particular polyanhydride polymerutilized and its molecular weight. The polyanhydride polymer may bebranched or linear. Examples of polyanhydrides which are useful in thepresent invention include homopolymers and copolymers of poly(lacticacid) and/or poly(glycolic acid), poly[bis(p-carboxyphenoxy)propaneanhydride] (PCPP), poly[bis(p-carboxy)methane anhydride] (PCPM),polyanhydrides of oligomerized unsaturated aliphatic acids,polyanhydride polymers prepared from amino acids which are modified toinclude an additional carboxylic acid, aromatic polyanhydridecompositions, and co-polymers of polyanhydrides with other substances,such as fatty acid terminated polyanhydrides, e.g., polyanhydridespolymerized from monomers of dimers and/or trimers of unsaturated fattyacids or unsaturated aliphatic acids. Polyanhydrides may be prepared inaccordance with the methods set forth in U.S. Pat. No. 4,757,128, herebyincorporated by reference. For example, polyanhydrides may besynthesized by melt polycondensation of highly pure dicarboxylic acidmonomers converted to the mixed anhydride by reflux in acetic anhydride,isolation and purification of the isolated prepolymers byrecrystallization, and melt polymerization under low pressure (10⁻⁴ mm)with a dry ice/acetone trap at a temperature between 140°-250° C. for10-300 minutes. High molecular weight polyanhydrides are obtained byinclusion of a catalyst which increases the rate of anhydride interchainexchange, for example, alkaline earth metal oxides such as CaO, BaO andCaCO₃.

Polyorthoester polymers may be prepared, e.g., as set forth in U.S. Pat.No. 4,070,347, hereby incorporated by reference.

Proteinaceous polymers may also be used. Proteinaceous polymers andtheir soluble derivatives include gelation biodegradable syntheticpolypeptides, elastin, alkylated collagen, alkylated elastin, and thelike. Synthetic polypeptides include poly-(N-hydroxyalkyl)-L-asparagine,poly-(N-hydroxyalkyl)-L-glutamine, copolymers ofN-hydroxyalkyl-L-asparagine and N-hydroxyalkyl-L-glutamine with otheramino acids. Suggested amino acids include L-alamine, L-tysine,L-phenylalanine, L-valine, L-tyrosine, and the like.

In embodiments where the polymer comprises a gel, one such usefulpolymer is a thermally gelling polymer, e.g., polyethylene oxide,polypropylene oxide (PEO-PPO) block copolymer such as Pluronic® F 1 27from BASF Wyandotte. In such cases, the local anesthetic formulation maybe injected via syringe as a free-flowing liquid, which gels rapidlyabove 30° C. (e.g., when injected into a patient). The gel system thenreleases a steady dose of local anesthetic at the site ofadministration.

In additional embodiments, the controlled release material, which ineffect acts as a carrier for the local anesthetic, can further include abioadhesive polymer such as pectins (polygalacturonic acid),mucopolysaccharides (hyaluronic acid, mucin) or non-toxic lectins or thepolymer itself may be bioadhesive, e.g., polyanhydride orpolysaccharides such as chitosan. Definitions or further descriptions ofany of the foregoing terminology are well known in the art and may befound by referring to any standard biochemistry reference text such as“Biochemistry” by Albert L. Lehninger, Worth Publishers, Inc. and“Biochemistry” by Lubert Stryer, W. H. Freeman and Company, both ofwhich are hereby incorporated by reference.

The aforementioned biocompatible hydrophobic and hydrophilic polymersare particularly suited for the methods and compositions of the presentinvention by reason of their characteristically low human toxicity andvirtually complete biodegradability.

In another embodiment, the carrier is a biocompatible, non-inflammatoryand nonbiodegradable polymer such as, e.g., ethylene vinyl acetate(“EVA”). Such a nonbiodegradable polymer permits inserted or injectedformulations to remain localized and able to be removed, intact, shouldthat be required. Biodegradable carriers soften and lose theirstructural integrity over time, making the task of emergency removaldifficult, if not impossible.

The substrates of the presently described formulations in certainpreferred embodiments are manufactured using a method that evenlydisperses the local anesthetic throughout the formulation, such asemulsion preparation, solvent casting, spray drying or hot melt, ratherthan a method such as compression molding. A desired release profile canbe achieved by using a mixture of polymers having different releaserates and/or different percent loading of local anesthetic and/orglucocorticosteroid agent, for example, polymers releasing in one day,three days, and one week. In addition, a mixture of microspheres havingone or more different local anesthetic agents, having the same ordifferent controlled release profile, can be utilized to provide thebenefits of different potencies and spectrum of activity during thecourse of treatment.

In a preferred embodiment, a slow release formulation is prepared asmicroparticles, e.g., microcapsules and/or microspheres in a sizedistribution range suitable for local infusion, infiltration and/orinjection. The diameter and shape of the microspheres or other particlescan be manipulated to modify the release characteristics. For example,larger diameter microspheres will typically provide slower rates ofrelease and reduced tissue penetration and smaller diameters ofmicrospheres will produce the opposite effects, relative to microspheresof different mean diameter but of the same composition. Optionally,other particle shapes, such as, for example, cylindrical shapes, canalso modify release rates by virtue of the increased ratio of surfacearea to mass inherent to such alternative geometrical shapes, relativeto a spherical shape. The diameter of injectable -microspheres are in asize range from, for example, from about 5 microns to about 200 micronsin diameter. In a more preferred embodiment, the microspheres range indiameter from about 20 to about 120 microns.

Methods for manufacture of microspheres are well known and are typifiedin the following examples. Examples of suitable methods of makingmicrospheres include solvent evaporation, phase separation and fluidizedbed coating.

In solvent evaporation procedures, the local anesthetic agent, ifsoluble in organic solvents, may be entrapped in the polymer bydissolving the polymer in a or volatile organic solvent, adding the drugto the organic phase, emulsifying the organic phase in water whichcontains less than 5% polyvinyl alcohol, and finally removing thesolvent under vacuum to form discrete, hardened monolithic microspheres.

Phase separation microencapsulation procedures are suitable forentrapping water soluble agents in the polymer to prepare microcapsulesand microspheres.

Phase separation involves coacervation of the polymer from an organicsolvent by addition of a nonsolvent such as silicone oil.

In fluidized bed coating, the drug is dissolved in an organic solventalong with the polymer. The solution is then processed, e.g., through aWurster air suspension coater apparatus to form the final microcapsuleproduct. Other methods of microsphere preparation are described inco-owned U.S. Ser. No. 08/714,783, filed on even date herewith, thedisclosure which is incorporated by reference herein in its entirety.

For example, the microspheres may be obtained by utilizing a solventextraction technique (reactor process) which involves dissolving thedrug and the polymer in an organic solvent such as ethyl acetate. Thissolution thereby obtained (the dispersed phase) is added to a solutionof, e.g., polyvinyl alcohol (PVA) in water (the continuous phase) withstirring. The emulsion thereby formed is then added to water in order toextract the solvent and to harden the microspheres. The mixture is thenfiltered and the microspheres are dried. One appropriate method ofdrying is, e.g., under vacuum at room temperature. Optionally, themicrosphere may be dried by a freeze drying process. The desiredparticle size fraction is then collected by sieving. The organic solventutilized is preferably ethyl acetate; however, any pharmaceuticallyacceptable organic solvent may be utilized, such as acetone, ethanol,diethyl ether, methanol, benzyl alcohol, methylene chloride, petroleumether or others. This procedure is particularly useful for preparingmicrospheres of e.g., bupivacaine base or free-base forms ofglucocorticoids.

Alternatively, the microspheres of bupivacaine base and/orglucocorticoid may be prepared by dissolving the drug and polymer inethyl acetate and thereafter spray drying the solution.

In instances where the microspheres are to incorporate drugs which arevery water soluble and insoluble in ethyl acetate, such as bupivacaineHCI and/or water soluble glucocorticoids, the microspheres may beprepared using a coacervation/phase separation rather than the solventextraction technique described above. However, the solvent extractiontechnique can be used with e.g., bupivacaine HCl and/or water solubleglucocorticoids due to its low water solubility at pH 7.4 and above. Thecoacervation/phase separation technique utilized involves dissolving thepolymer in ethyl acetate and suspending micronized bupivacaine HCl inthe solution. Silicone oil is then added to-form the microspheres. Thismixture is then added to heptane to harden the microspheres, which arethen separated by filtration. The microspheres are dried under a vacuumat room temperature. The desired particle size fraction is thencollected by sieving.

Alternatively, micropheres prepared using bupivacaine HCI and/orglucocorticoids may be accomplished by suspending the drug in a solutionof polymer in ethyl acetate or in methylene chloride and methanol andspray drying.

Alternatively, the drug or drugs may be dissolved in water, and thepolymer may be dissolved in ethyl acetate. The water phase then can beadded to the organic phase and either homogenized or sonicated to yielda W/O emulsion. The drug being in the water phase would then besurrounded by polymer (oil phase). This is then added, e.g., pairedinto, PVA solution in water with homogenization to form a W/O/Wemulsion. The solvent diffuses out, leaving microspheres. Additionalcold water can be added to harden the microspheres. This process mayyield more uniform microspheres without requiring micronization of thedrug. Also, as the drug will be surrounded by polymer, the release ofthe drug may be more uniform and be diffusion-controlled.

The biocompatible controlled release materials may optionally be used inorder to prepare controlled release local anesthetic implants. Theimplants may be manufactured, e.g., by compression molding, injectionmolding, and screw extrusion, whereby the local anesthetic agent isloaded into the polymer. Implantable fibers can be manufactured, e.g.,by blending the local anesthetic agent with the controlled releasematerial and then extruding the mixture, e.g., under pressure, tothereby obtain biocompatible fibers. In certain preferred embodiments,the glucocorticosteroid agent may be incorporated into the implant, ormay be coated onto a surface of the implant.

In other embodiments of the invention, the controlled release materialand/or carrier comprises, pharmaceutically acceptable emulsions,including oil in water and water in oil emulsions, gels, gums andmatrices suitable for controlled release of local anesthetics and/orglucocorticoids an artificial lipid vesicle, or liposome. Simply by wayof example, liposomes are well known in the art as carriers of bioactiveor pharmacologically active substances such as drugs. Liposomes asdescribed herein will vary in size. Preferably, the liposomes have adiameter between 100 nm and 10 microns or greater. A wide variety oflipid materials may be used to form the liposomes including naturallecithins, e.g., those derived from egg and soya bean, and syntheticlecithins, the proviso being that it is preferred that the lipids arenon-immunogenic and biodegradable. Also, lipid-based materials formed incombination with polymers may be used, such as those described in U.S.Pat. No. 5,188,837 to Domb, (incorporated by reference herein in itsentirety).

Examples of synthetic lecithins which may be used together with theirrespective phase transition temperatures, aredi-(tetradecanoy)phosphatidylcholine (DTPC) (23° C.),di-(hexadecanoyl)phosphatidylcholine ODBPC) (41° C.) anddi-(octandecanoyl) phosphatidylcholine (DOPC) (55° C.).Di-(hexadecanoyl) phosphatidycholine is preferred as the sole or majorlecithin, optionally together with a minor proportion of thedi-(octadecanoyl) or the di-(tetradecanoyl) compound. Other syntheticlecithins which may be used are unsaturated synthetic lecithins, forexample, di-(oleyl)phosphatidyl-choline anddi-linoleyl)phosphatidylcholine. In addition to the mainliposome-forming lipid or lipids, which are usually phospholipids, otherlipids (e.g. in a proportion of 5-40% w/w of the total lipids) may beincluded, for example, cholesterol or cholesterol stearate, to modifythe structure of the liposome membrane, rendering it more fluid or morerigid depending on the nature of the main liposome-forming lipid orlipids.

In certain embodiments, the glucocorticosteroid agent is incorporatedalong with the local anesthetic agent into the lipid. In other preferredformulations, the lipids containing the local anesthetic agent aredispersed in a pharmaceutically acceptable aqueous medium. Theglucocorticosteroid agent may be incorporated into this aqueous medium.In a further embodiment, a portion of the dose of the local anestheticis incorporated into the aqueous medium in immediate release form. Theresultant formulation is an aqueous suspension which may comprise thelocal anesthetic and/or glucocorticosteroid agent partitioned between afree aqueous phase and a liposome phase.

As an even further alternate embodiment, liposomes containing localanesthetic may be combined in an aqueous phase where liposomescontaining the glucocorticosteroid agent to form an aqueouspharmaceutical suspension useful for administration at the desired sitein the patient to be anesthetized. This may be accomplished viainjection or implantation. Liposomes may be prepared by dissolving anappropriate amount of a phospholipid or mixture or phospholipidstogether with any other desired lipid soluble components (e.g.,cholesterol, cholesterol stearate) flowing in a suitable solvent (e.g.,ethanol) and evaporating to dryness. An aqueous solution of the localanesthetic, optionally with glucocorticosteroid agent, may then be addedand mixed until a lipid film is dispersed. The resulting suspension willcontain liposomes ranging in size, which may then fractionated to removeundesirable sizes, if necessary. This fractionation may be effected bycolumn gel chromatography, centrifugation, ultracentrifugation or bydialysis, as well known in the art.

The above method of preparation of liposomes is representative of apossible procedure only. Those skilled in the art will appreciate thatthere are many different methods of preparing liposomes, all of whichare deemed to be encompassed by the present disclosure.

In additional embodiments of the invention, the substrate comprises aplurality of microcapsules laden with the local anesthetic agent with orwithout the glucocorticosteroid agent. Microcapsules may be prepared,for example, by dissolving or dispersing the local anesthetic agent inan organic solvent and dissolving a wall forming material (polystyrene,alkylcelluloses, polyesters, polysaccharides, polycarbonates,poly(meth)acrylic acid ester, cellulose acetate,hydroxypropylmethylcellulose phthalate, dibutylaminohydroxypropyl ether,polyvinyl butyral, polyvinyl formal, polyvinylacetal-diethylaminoacetate, 2-methyl-5-vinyl pyridine methacrylate-methacrylic acidcopolymer, polypropylene, vinylchloride-vinylacetate copolymer, glyceroldistearate, etc.) in the solvent; then dispersing the solvent containingthe local anesthetic agent and wall forming material in acontinuous-phase processing medium, and then evaporating a portion ofthe solvent to obtain microcapsules containing the local anestheticagent in suspension, and finally, extracting the remainder of thesolvent from the microcapsules. This procedure is described in moredetail in U.S. Pat. Nos. 4,389,330 and 4,530,840, hereby incorporated byreference.

The controlled release dosage forms of the present invention preferablyprovide a sustained action in the localized area to be treated. Forexample, it would be desirable that such a formulation provideslocalized anesthesia to the site for a period of one day, two days,three days, or longer. The formulations can therefore, of course, bemodified in order to obtain such a desired result.

Microspheres and other injectable substrates described herein may beprepared incorporated with a pharmaceutically acceptable solutionvehicle, such as a isotonic saline and/or other buffer aqueous solutionor suspension for injection. The viscosity of the final reconstitutedproduct is preferably in a range suitable for the route ofadministration. In certain instances, the final reconstituted productviscosity may be, e.g., about 35 cps. Administration may be via thesubcutaneous or intramuscular route. However, alternative routes arealso contemplated, and the formulations may be applied to the localizedsite in any manner known to those skilled in the art including topicalapplication, localized injection or infiltration, localized intraarterial nerve block, and the like, such that a localized effect isobtained. The substrate formulations of the invention can alsooptionally be implanted, e.g., surgically or by means of a probe, at thesite to be treated. Thus, the formulations of the present invention,when including a local anesthetic, may be used in the control ofpost-operative pain.

Depending on the potency of the desired local anesthetic and upon thedesired weight of the resulting formulation, the anesthetic isincorporated into the polymer or other controlled-release formulation ina percent loading between 0.1% and 90% by weight. Preferably theanesthetic is incorporated as a high load formulation comprising fromabout between about 30% loading to about 90% loading by weight.Preferably, a high load comprises from about 60% to about 85% by weight,loading or even from about 70% to about 80% loading by weight. Mostpreferably, a high load comprises about 75% loading, by weight, of localanesthetic agent.

It is also possible to tailor a system to deliver a specified loadingand subsequent maintenance dose by manipulating the percent drugincorporated in the polymer and the shape of the matrix or formulation,in addition to the form of local anesthetic (e.g., free base versussalt) and the method of production. Heretofore it has been believed thatthe amount of drug released per day increases proportionately with thepercentage of drug incorporated into the formulation, e.g., matrix (forexample, from 5 to 10 to 20%). Based on this previously observedproportional relationship the ordinary artisan would have previouslybelieved that high loadings of drug would result in rapid release ordumping of the local anesthetic at the injection or implantation site,resulting a shortened of action and unacceptable levels of local tissueirritation or even local tissue toxicity.

However, in a surprising discovery, it has been found that at high drugloadings according to the present invention, the proportionalrelationship between drug loading and release rates does not apply. Forexample, according to the preferred embodiment, polymer matrices orother formulations with about 75% drug incorporated are utilized toprovide both a rapid onset of local anesthesia and a prolonged releaseof local anesthesia. It is also possible to incorporate substantiallymore drug, depending on the drug, the method used for making and loadingthe carrier, e.g., a controlled release polymer so that an acceptablerelease rate is obtained. The use of glucocorticosteroid to prolong thelocal anesthesia further enhances the unexpectedly beneficial result ofusing high drug loadings.

When a glucocorticosteroid agent is included in the controlled releasesubstrates comprising local anesthetic, it has been found that usefulloadings of glucocorticosteroid agent are, e.g., from 0.005% to 30% byweight of the substrate.

When the glucocorticosteroid agent is included with a suitable vehiclein which microparticles comprising local anesthetic are suspended, theglucocorticosteroid agent is present, for example, in a weight percentrelative to the local anesthetic varying from about 0.005% to about 15%.

The artisan will appreciate that the dosage of the controlled releaseformulations is dependent upon the kind and amount of the drug to beadministered, the recipient animal, and the objectives of the treatment.For example, when the drug included in the microspheres of the presentinvention is bupivacaine, the bupivacaine content of the formulationranges from, e.g., about 0.5 to about 450 mg/kg body weight. Theeffective dose of bupivacaine, or an amount of another local anestheticsufficient to provide proportional potency, can range from about 1 toabout 600 mg, or more, of bupivacaine injected or inserted at each sitewhere the release of a local anesthetic agent is desired. In certainpreferred embodiments, the dose of bupivacaine in the controlled releasedosage form of the invention is sufficient to provide a controlledrelease of about 8 to about 30 mg per hour at the release site for atleast 1 to 4 days. Since the formulations of the present invention arecontrolled release, it is contemplated that formulations may includemuch more than usual immediate release doses, e.g., as much as 120 mg ofdrug per kg of body weight, or more.

In certain preferred embodiments, the controlled release substratecomprising local anesthetic is characterized by in vitro release ratesof about 10 to about 60 percent release of local anesthetic after 24hours, from about 20 to about 80 percent release after 48 hours and fromabout 40 to about 100 percent release, after 72 hours. More preferably,the controlled release substrate comprising local anestheticscharacterized by in vitro release rates of about 25 to about 40 percentrelease of local anesthetic after 24 hours, from about 40 to about 50percent release after 24 hours and from about 45 to about 55 percentrelease after 72 hours and 80 to 100 percent cumulative release isprovided after about 280 hours.

In order to obtain a prolonged local anesthetic effect in vivo whencombined with the glucocorticosteroid agent as described herein, theglucocorticosteroid agent is placed into approximately the same site ina patient (e.g., human or veterinary) before, simultaneously with, orafter the placement of a local anesthetic at that site. The presence ofglucocorticosteroid agent in the controlled release formulation does notsignificantly affect the in vitro or in vivo release rates of localanesthetic.

In a preferred embodiment the local anesthetic effect is prolonged bythe use of an glucocorticosteroid agent from about 1.1 to about 14 foldor more of the duration local anesthetic effect that is obtained fromthe same formulation without benefit of an glucocorticosteroid agent. Ina further preferred embodiment, the prolongation ranges from about 1 toabout 13 fold, or even from about 6 to about 13 fold of the duration oflocal anesthesia induced by controlled release local anesthetic withoutglucocorticosteroid enhancement.

The duration of the local anesthetic effect prolonged by anglucocorticosteroid agent ranges, e.g., from about 0.1 to about 200hours or more, from about 1 to about 150 hours, from about 24 to about150 hours and from about. 24 to about 100 hours, of local anesthesiafrom the time of administration of the local anesthetic.

The rate of release of local anesthetic agent or other drugsincorporated into the formulation will also depend on the solubilityproperties of the local anesthetic or drug. The greater the solubilityin water, the more rapid the rate of release in tissue, all otherparameters being unchanged. For example, those local anesthetic agentshaving pH dependent solubility will be released more rapidly at theoptimum pH for those compounds. The greater the solubility in water, themore rapid the rate of release in tissue, all other parameters beingunchanged. For example, those local anesthetic agents having pHdependent solubility will be released more rapidly at a pH lower thanthe pKa value for each such compound. For example, in one embodiment,the formulation will have released, in vitro, at least 70 percent of alocal anesthetic at 48 hours at about pH 6 and will have released atleast 40 percent of a local anesthetic at a pH ranging from about 7.4 toabout 8, at 48 hours. Other combinations are pH independent in theirrelease.

The examples demonstrate that the above-described glucocorticosteroidagents prolong the duration of local anesthesia in vivo and do notsignificantly alter the time course of release of bupivacaine in vitro.

Potential applications include any condition for which localizedanesthesia is desirable. This includes both the relief of pain and motorsymptoms as well as local anesthesia, e.g., localizes inhibition ofnerve transmission, for other medical purposes. The formulations andmethods according to the invention can be used to provide two to fiveday intercostal anesthesia for thoracotomy, or longer term intercostalanesthesia for thoracic post-therapeutic neuralgia, lumbar sympatheticanesthesia for reflex sympathetic dystrophy, or three-dayilioinguinal/iliohypogastric blockade for hernia repair.

Other potential applications include obstetrical or gynecologicalprocedures. Yet further potential applications include providinglocalized temporary sympathectomy, e.g., blockade of sympathetic orparasympathetic ganglia to treat a variety of autonomic diseases,including circulatory dysfunction or cardiac dysrhythmias. Theformulations may also be used to treat trigeminal neuralgia and otherdiseases of the cranial nerves as well as to provide temporary nerveblockade to treat localized muscle spasm and treatment of retrobulbarconditions, e.g., eye pain. Other uses include intra-operativeadministration in order to reduce pain during and after the operativeprocedure, especially for plastic surgery procedures where prolongedanesthesia will enhance the outcome.

These systems can also be used for the management of various forms ofpersistent pain, such as postoperative pain, sympathetically maintainedpain, or certain forms of chronic pain such as the pain associated withmany types of cancer.

These systems may also be used for anesthetizing nociceptive pathways(afferent and efferent) in patients with acute pancreatitis, ileus, orother visceral disorders. These are merely examples, and additional usesfor both human and veterinary practice are immediately apparent to theartisan.

Methods of Administration

Further to the above discussion, it will be appreciated that, in apreferred method of administration a dosage form, e.g., microspheres,are administered topically e.g., by application and/or by infusion,infiltration and/or injection into a site where local anesthetic agentis to be released. Microspheres may be injected through a syringe or atrochar. Dosage forms such as pellets, slabs, spheroids and the like mayalso be optionally surgically placed into a site where release of oralanesthetic agent is desired.

As described below, microspheres according to the invention can beadministered alone or in combination with a carrier including aglucocorticosteroid agent, e.g., dissolved and/or suspended in acarrier, e.g., as a solution or suspension in an amount effective toprolong the duration of local nerve blockade. Alternatively, themicrospheres include an amount of glucocorticosteroid agent effective toprolong the duration of local nerve blockade.

In another alternative, one or more glucocorticosteroid agents can beadministered before, simultaneously with or after administration of thecontrolled release local anesthetic, wherein the glucocorticosteroid isformulated into a separate microsphere formulation for controlledrelease. The controlled release rate for the glucocorticosteroid agentsmay be the same as or different than the controlled release rate for thelocal anesthetic. In a further embodiment, it has been found thatadditional dose of glucocorticosteroid agent may also be administered asan injectable solution or suspension, in an injectable carrier or in acontrolled release carrier to the nerve to be blockaded after thecontrolled release local nerve blockade has worn off, in order toreactivate the initial nerve blockade without the co-administration ofadditional local anesthetic.

The microspheres may be prepared from PLGA polymers ranging from, forexample, PLGA in a ratio of 50:50, 65:35 or 75:25. An optimumcomposition has been determined to be PLGA 65:35.

The artisan will appreciate that, as with all local anesthetics, thedosage of local anesthetic containing microspheres will vary and willdepend, simply by way of example, upon the area to be anesthetized, thevascularity of the tissues, the number of neuronal .segments to betreated, the size and weight of the patient (e.g., veterinary practice,human child, human adult) individual tolerance and the technique ofanesthesia. Of course, under normal circumstances, the lowest dosageneed to provide effective anesthesia should be administered.

The microspheres, formulated with, e.g., PLGA 65:35 microspheres areadministered in a dose ranging from, for example, 1 through 450 mg perkg of body weight, of microspheres 75% (w/w) loaded with a localanesthetic such as bupivacaine, per kg of body weight. In a preferredembodiment the dose ranges from 5 through 250 mg of microspheres/kg ofbody weight. In a more preferred embodiment the dose ranges from about10 to about 150 mg of microspheres/kg of body weight, with PLGA 65:35.

An effective dose of a local anesthetic, such as bupivacaine, istypically administered in microspheres comprising, e.g., 75% by weightbupivacaine, and can range from about 0.5 to about 1000 mg, or more, ofbupivacaine, depending on the site to be anesthetized, the number ofsegments to be anesthetized and the patient, as discussed above.Preferably, a dose ranging from about 1 mg to about 500 mg ofbupivacaine is administered, or even a dose ranging from about 5 mg toabout 100 mg of bupivacaine is administered at the site and/or sites tobe anesthetized.

Certainly, the artisan will appreciate the fact that the dose rangesmentioned above are based on the potency of bupivacaine, and that exacteffective dosages will vary will the particular relative potency andpharmacokinetics of each local anesthetic and will be able to readilyadjust the dose according to the degree of anesthesia experienced by thepatient.

The formulation described herein can also be used to administer localanesthetic agents that produce modality-specific anesthesia, as reportedby Schneider, et al., Anesthesiology, 74:270-281 (1991), or that possesphysical chemical attributes that make them more useful forsustained-release then for single injection anesthesia, as reported byMasters, et al., Soc. Neurosci. Abstr. 18:200 (1992), the teachings ofwhich are incorporated herein.

Administration of formulations according to the invention may requirethe use of a vehicle, e.g., any vehicle that is pharmaceuticallyacceptable for desired route of administration. Thus, for topicaladministration or application, the formulations prepared according tothe invention comprising local anesthetic and/or glucocorticoid may bedissolved e.g., for immediate release forms) or suspended (e.g., formicroparticles) in vehicles including buffered solutions, e.g., salinesolution, including, e.g, hypotonic and/or buffered saline, as well asin creams, ointments, oils, emulsions, liposomes and the like and/or anyother art-known pharmaceutically acceptable topical vehicle. Foradministration by injection and/or infiltration, the formulationsaccording to the invention may be suspended (e.g., for microparticles),or dissolved (e.g., for immediate release forms), in any art-knownvehicle suitable for injection and/or infiltration. Such vehiclesinclude, simply by way of example, isotonic saline, buffered orunbuffered and the like and may optionally include any other art knowningredients or agents, e.g., colorants, preservatives, antibiotics,epinephrine and the like. A more complete listing of art-known vehiclesfor administration of formulations topically, by systemic administrationand/or local injection and/or-infiltration is provided by referencetexts that are standard in the art, for example, REMNGTON'sPHARMACEUTICAL SCIENCES, 16th Edition, 1980 and 17th Edition, 1985, bothpublished by Mack Publishing Company, Easton, Pa., the disclosures ofwhich are incorporated by reference herein in their entireties.

The use of the above-described glucocorticosteroid agents before,simultaneously with or after administration of a high load formulationof a controlled release local anesthetic, results in prolongedanesthesia relative to the derivation of anesthesia induced by anequivalent formulation without co-administration of glucocorticoid.

Clinical Utility

It will also be appreciated that the high load local anestheticformulations and methods according to the invention can generallyemployed in any art known localized anesthesiological procedures. Forexample, for surface anesthesia, microparticle suspensions or otherforms of controlled release carrier, e.g., microsphere, cellulose basedpolymers and/or gum matrices in paste form, suitable for topicalapplication, are used to anesthetize mucous membranes, skin and forophthalmological use. Effective amounts of glucocorticoid agents can beincluded with the topical controlled release formulation or, optionally,at least a portion of the glucocorticoid agent can be separatelyadministered in controlled release form, immediate release form and/or acombination thereof.

In addition, the high load local anesthetic formulations and methodsaccording to the invention can be used for infiltration anesthesia,wherein a formulation suitable for injection is injected directly intothe tissue requiring anesthesia. For example, an effective amount of theformulation in injectable form is infiltrated into a tissue area that isto be incised or otherwise requires local anesthesia. In addition, thelocal anesthetic formulations and methods according to the invention canbe used for field block anesthesia, by injecting an effective amount ofthe formulation in injectable form in such a manner as to interruptnerve transmission proximal to the site to be anesthetized. Forinstance, subcutaneous infiltration of the proximal portion of the volarsurface of the forearm results in an extensive area of cutaneousanesthesia that starts 2 to 3 cm distal to the site of injection. Simplyby way of example, the same effect can be achieved for the scalp,anterior abdominal wall and in the lower extremities. Effective amountsof glucocorticoid agents can be included with injectable controlledrelease formulation or, optionally, at least a portion of theglucocorticoid agent can be separately administered in controlledrelease form, immediate release form and/or a combination thereof.

Further, for even more efficient results, the high load local anestheticformulations and methods according to the invention can be used fornerve block anesthesia. For example, an effective amount of theformulation in injectable form is injected into or adjacent toindividual peripheral nerves or nerve plexuses. Injection of aneffective amount of a high load local anesthetic formulation accordingto the invention into mixed peripheral nerves and nerve plexuses canalso desirably anesthetize somatic motor nerves, when required. The highload formulations and methods according to the invention can also beused for intravenous regional anesthesia by injecting apharmacologically effective amount of microspheres in injectable forminto a vein of an extremity that is subjected to a tourniquet to occludearterial flow.

Further still, spinal and epidural anesthesia using high loadformulations, e.g., injectable microspheres and methods according to theinvention will be appreciated by the artisan to be within the scopecontemplated by the present invention.

The formulation described herein can also be used to administer localanesthetic agents that produce modality-specific blockade or anesthesiaeffect, as reported by Schneider, et al., Anesthesiology, 74:270-281(1991).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following non-limiting examples illustrate the preparation of theformulations according to the invention and the effects of localanesthetic and glucocorticosteroid agents alone and in combination.

Example 1

Prolonged nerve blockade with steroidal anti-inflammatories

As demonstrated by the following study:

(1) Bupivacaine-polyester microspheres can be formulated with mechanicalstability at very high percent drug loading, for example, up to 75% byweight.

(2) Bupivacaine-polyester microspheres with high percent loading havecontrolled release of drug, and do not produce rapid initial burstrelease of drug in vitro or in vivo.

Methods and Material

Abbreviations include PLGA, poly-lactic-glycolic acid; CH₂Cl₂, methylenechloride; dpm, disintegrations per minute; cpm, counts per minute; rpm,revolutions per minute.

The non-radioactive polymer microspheres used in this study wereobtained from a commercial source. Tritium labeled dexamethasone wasobtained from Amersham (specific activity 9.24×10¹⁰ dpm/μmole).Bupivacaine free base was supplied by Purdue Frederick and dexamethasonewas supplied by Sigma. Trisma base was supplied by Sigma. Dulbecco'sphosphate-buffered saline was supplied by Gibco, Md. (KCL 2.68 mM/L,KH₂PO₄ 1.47 mM/L, NaCl 547.5mM/L, NaBPO₄ 9.50 mM/L). The suspensionmedia used in the in vivo experiments was consisted of 0.5% w/v sodiumcarboxymethylcellulose (medium viscosity) and 0.1% w/v Tween 80. ACoulter® Multisizer II, Coulter Electronics Ltd., Luton, England wasused to determine the mass median diameter of the microspheres.

Polymer synthesis and Local Anesthetic Incorporation

The radiolabeled microspheres were formulated by a single emulsiontechnique, using an evaporation process. Two types of radiolabeledmicrospheres were formulated, one which contained 75% w/w unlabeledbupivacaine and 0.05% w/w tritium labeled dexamethasone and the othercontained 0.05% w/w unlabeled dexamethasone and 75% w/w tritium labeledbupivacaine. The micro spheres which contained tritium labeleddexamethasone were prepared as follows: an aliquot of dexamethasonecontaining 8×10⁶ disintegrations per minute (dpm) was added to 100 μlsof a solution of 5 mg of unlabeled dexamethasone in 5 mls of ethanol.The sample was dried under a stream of nitrogen for one hour and 50 mgof PLGA 65:35 and 150 mg of bupivacaine free base in 1 ml of CH₂CL₂ wereadded. The tube was vortexed for 1 minute at 2000 rpm on a FisherScientific Touch Mixer, Model 232. Then 1 ml of 0.3% polyvinylalcohol in100 mM Trisma®D (tris(hydroxymethyl)amino methane) base (pH adjusted to8.4) was added, and an emulsion formed by vortexing for 45 seconds. Theemulsion was then poured into 100 mls of 0.1% polyvinylalcohol in 100 mMTrisma® base. The CH₂CL₂ was removed from the microspheres using arotary evaporator under vacuum at 31° C. for 20 minutes. After 2-3minutes bubbles formed indicated that the organic solvent was beingremoved. The microspheres were sieved through a series of stainlesssteel sieves of pore sizes 140μ, 60μ and 20μ (Neward Wire Co.). Thosemicrospheres which were less than 20 and greater than 140 microns indiameter were discarded. The microspheres which fell in the size range20μ to 140μ were centrifuged at 4000 rpm for 5 minutes, rinsed withbuffer and centrifuged again. The microspheres were then frozen inliquid nitrogen and lyophilized overnight. The microspheres wereexamined before and after solvent removal using an American OpticalOne—Ten light microscope to ensure that no leaching of the drug tookplace. If leaching did occur, the bupivacaine crystallized and could beseen even at 10× using a light microscope.

The microspheres which contained tritium labeled bupivacaine wereformulated as described above with the following exceptions: An aliquotof radiolabeled bupivacaine consisting of 9×10⁶ dpm was added to 150 mgof unlabeled bupivacaine free base. The solution was then vortexed toensure homogeneous mixing of labeled and unlabeled bupivacaine. Theethanol was then removed under a stream of nitrogen for 1 hour. Uponremoval of the ethanol, 50 mg of PLGA 65:35 and 100 μl from a solutiondexamethasone 1 mg/ml in ethanol were added. Thereafter, the protocolwas the same as that used to formulate microspheres which containedradiolabeled dexamethasone.

In order to determine the drug content, 5 mg of microspheres weredissolved in 2 mls of CH₂Cl₂ and the local anesthetic concentrationdetermined by U.V. spectroscopy. The absorbance at 272 nm was read andcompared to a. calibration curve of known amounts (0 to 2.5 mg/ml) ofbupivacaine free base dissolved in CH₂CI₂.

In Vitro Release studies

Unlabeled Microspheres

5 mg of microspheres were weighed out and 2 mls of Dulbecco'sphosphate-buffered saline was added. The pH of the buffer was adjustedto 7.4 and 0.1% sodium azide was added as an antimicrobial agent. Thebuffer was changed at 0.5, 2, 6, 12, and 24 hours and once dailythereafter. The amount of bupivacaine free base in the buffer wasdetermined using a Hewlett Packard 8452 Diode Array Spectrophotometer at272 nm. Duplicates from each batch of microspheres were assayed. Releasemedia incubated with control microspheres which did not containbupivacaine showed insignificant absorbance at 272 nm.

Labeled Microspheres

The procedure used to determine the in vitro release of both bupivacaineand dexamethasone is the same as that used for non-radiolabeledmicrospheres, except that the amount of radiolabeled compound releasedinto the buffer was determined by adding 17 mls of Ecolume®scintillation fluid to 2 mls of buffer. The total number of counts wasdetermined using a LKB Wallac 1214 Rackbeta Liquid ScintillationCounter. The efficiency, (the counts per minute/disintegration perminute), of the counter was determined to be 51%. Five replications ofeach set of radiolabeled microspheres were used.

Preparation of Microsphere Suspensions for In Vivo Testing

The dose used varied between 50 and 450 mg of drug/kg of rat, and 0.6mls of injection vehicle was used for each injection. The injectionvehicle consisted of 0.5% w/w sodium carboxy methyl cellulose and 0.1%w/w Tween 80 in water. The microspheres in the suspending media werevortexed at maximum speed for two minutes prior to injection. Theinjection was performed by locating and injecting slightly below andproximal to the greater trochanter. Rats were anesthetized withhalothane 2-3% inspired concentration in oxygen during injections, atleast five rats were used to test each formulation.

Testing for Sciatic Nerve Block or Anesthesia Effect

Male Sprague-Dawley Charles River rats weighing between 200 and 350 mgwere used to determine the duration of the block obtained with each ofthe different microsphere formulations tested. They were handled dailyand habituated to the testing paradigm prior to exposure to localanesthetic injections. Sensory and motor blockade or anesthesia effectwere examined as described above. The duration of the sensory block wasdetermined as the length of time for which the latency was greater thanor equal to 7 seconds.

In addition to sensory testing, motor testing was performed at each timepoint to examine the rat's ability to hop and to place weight on itshind leg. Animals were handled and cared for according to institutional,state, and federal regulation, and according to the guidelines of theInternational Association for the Study of Pain, Seattle, Wash.

RESULTS

Microsphere morphology

Using the preparative procedures outlined above, smooth, spherical,mechanically stable microspheres were produced without significantquantities of crystalline bupivacaine leaching out the microspheres.When the drug leached out of the microspheres into the aqueous solution,it was in the form of long crystals, approximately 30μ in length and wasvisible by light microscopy. Comparison of PLGA microspheres loaded with75% bupivacaine and 0.05% dexamethasone formulated by solvent removalusing a vacuum at 40° C. with those formulated by stirring themicrospheres at room temperature and pressure, for three hours until theorganic solvent evaporated, showed significant differences. Increasingthe rate of removal of the organic solvent using heat and vacuum reducedthe rate of leaching of bupivacaine out of the microspheres.

In vitro release kinetics

FIG. 7 is a graph of % cumulative release of bupivacaine from PLA andPLGA copolymers, PLGA 50:50, 75:25, and 65:35, over time. The resultsdemonstrate that there is. a burst of release of drug from PLAinitially, which is substantially less in the PLGA copolymers.

Other polymers have been tested. Ethyl cellulose andpolyhydroxyvalerate-butyrate (“PHBV”) microspheres (20 to 140 microns indiameter) containing 50 and 75% by weight bupivacaine, with or without0.05% dexamethasone, showed different respective release rates. Ethylcellulose microspheres released 31% bupivacaine during the first day andPHBV microspheres released 70% bupivacaine in during the first day, withefficacy confirmed by in vivo studies.

The similar in vivo latency durations resulting from bupivacaineencapsulated into PLGA 50:50, 65:35, 75:25 PLGA and PLA are shown inFIGS. 4A-4D Comparison of the % cumulative release of bupivacaine frommicrospheres when the pH of the buffer media was 6, 7.4 and 8 shows thatthe rate of release of bupivacaine was higher at pH 6 than at pH 7.4 or8, because bupivacaine has greater water solubility at pH 6 than at pH7.4 or pH 8 (data not shown).

Radiolabeled Microspheres

When microspheres loaded with unlabeled bupivacaine and radiolableddexamethasone were prepared, the yield (weight of microspheres/weight ofbupivacaine+weight of polymer) was 45%. The bupivacaine content wasdetermined to be 75±1%. When microspheres loaded with unlabeleddexamethasone and radiolabeled bupivacaine were prepared, the yield was50%, and the bupivacaine content was 73±2%. Comparisons of the percentcumulative release of both tritium labeled dexamethasone and tritiumlabeled bupivacaine, proves that dexamethasone was incorporated into themicrospheres and that both substances were released at similar releaserates.

Rat Sciatic Nerve Blockade In Vivo

In order to determine the toxic response of the rats to variousmicrosphere doses, the rats were injected with concentrations rangingfrom 50 to 450 mg of bupivacaine/kg of rat for each 100 polylactic acid(PLA), polylactic, polyglycolic acid copolymer (“PLGA”) 65:35 and 75:25(FIG. 2). No systemic toxicity, excessive sluggishness or death wasobserved even at the highest doses.

A comparison of the latencies and mean motor times obtained from PLGA65:35 microspheres which contained 0.0%, 0.005% and 0.05% dexamethasone,respectively, at a dose of 150 mg bupivacaine/kg of rat provided nerveblock durations of 8, 50 and 170 hours, respectively (FIG. 3A) anddecreased motor skills (FIG. 3B) with, respectively. The optimum doseand formulation was determined to be 150 mg of drug/kg of rat of PLGA65:35 microspheres loaded with 75% bupivacaine and 0.05% dexamethasone,as this was the lowest dose which resulted in the longest duration ofblock.

The presence of 0.05% dexamethasone or betamethasone in the injectionfluid significantly prolonged the duration of sensory (FIG. 5A) andmotor (FIG. 5B) sciatic nerve block (FIGS. 5A-5B). Similarly, thepresence of dexamethasone, betamethasone, methylprednisolone orhydrocortison in microspheres also significantly prolonged the durationof sciatic nerve block (e.g., see FIG. 6). That is, the block oranesthesia effect obtained using microspheres which contained, e.g.,0.05% dexamethasone was up to 13 fold longer than the block oranesthesia effect obtained using the corresponding microspheres whichdid not contain any dexamethasone. It was determined that 150 mg ofmicrospheres /Kg of rat was the optimum dosage and produced the greatestprolongation of block.

The duration of sensory block for groups of rats injected withbupivacaine loaded PLA 100, PLGA 75:25, PLGA 65:35 and PLGA 50:50microspheres, with and without incorporated dexamethasone was compared.In each case, the presence of dexamethasone in the microspheres resultedin a 6-13 fold increase in. the duration of block (see FIGS. 4A-D). Meansciatic nerve block durations among treatment groups varied from 65±3 to134±13 hours for microsphere formulations which contained dexamethasone.Control groups receiving injections of polymer microspheres containingno drug or dexamethasone or containing dexamethasone alone showed nosensory or motor block.

The in vitro results showed that the bupivacaine was released from themicrospheres in a controlled manner. In general, 24-40% of thebupivacaine was released in the first 24 hours, and approximately 7%released daily thereafter. After 5-8 days approximately 90% of thebupivacaine was released. The presence of dexamethasone in themicrospheres did not significantly affect the in vitro release rates ofbupivacaine (e.g., see FIG. 1) and the in vitro results cannot accountfor the prolongation of block, due to the presence of dexamethasoneobserved in vivo.

Example 2

Animal Testing Procedures

The following methods were utilized in the in vivo studies on rats. Therats were kept at room temperature (e.g., 22-25° C.), unless otherwiseindicated.

Nerve Block Tests

Motor Anesthesia

The rats were behaviorally tested for sensory and motor blockade oranesthesia effect in a quiet observation room. Testing was onlyperformed in rats showing appropriate baseline hot plate latencies afterat least one week of testing. In all testing conditions, theexperimenter recording the behavior was unaware of the side containingthe local anesthetic. To assess motor block or anesthesia, a 4-pointscale based on visual observation was devised. (1) normal appearance,(2) intact dorsiflexion of foot with an impaired ability to splay toeswhen elevated by the tail, (3) toes and foot remained plantar flexedwith no splaying ability, and (4) loss of dorsiflexion, flexion of toes,and impairment of gait. For graphing clarity, partial motor block equalsa score of 2 and dense motor block is a score of either 3 or 4.

Sensory Anesthesia

Sensory blockade or anesthesia effect was measured by the time requiredfor each rat to withdraw its hind paw from a 56° C. plate (IITC LifeScience Instruments, Model 35-D, Woodland Hills, Calif.). They weretested daily at standard room temperature and allowed to adjust to theirsurroundings in a quiet room for at least 30 minutes before testing,also at room temperature. The rats were held with a cloth gently wrappedabove their waist to restrain the upper extremities and obstruct vision.The rats were positioned to stand with one hind paw on a hot plate andthe other on a room temperature plate. With a computer data collectionsystem (Apple IIe with a footpad switch), latency to withdraw each hindpaw to the hot plate was recorded by alternating paws and allowing atleast fifteen seconds of recovery between each measurement. If nowithdrawal occurred from the hot plate within 12 seconds, the trial wasterminated to prevent injury and the termination time was recorded.Testing ended after five measurements per side, the high and low pointswere disregarded, and the mean of the remaining three points wascalculated for each side. Animals were handled in accordance withinstitutional, state and federal guidelines.

No rats were observed to have inflammation or blisters (data fromformlation in the form of surgically implanted pellets). Rats weretested for at least two weeks prior to surgery to insert the implants toachieve a consistent baseline latency, and testing continued for twoweeks after surgery to confirm complete recovery from sensory blockadeor anesthesia effect. Motor blockade or anesthesia effect was rated on a4-point scale. Animals with a motor block or anesthesia effect 4 had aclubbed hindpaw and usually dragged their affected leg when walking.Motor block or anesthesia effect 3 animals walked normally but had toesthat failed to splay when the animal was lifted. Animals with motorblock or anesthesia effect of 2 showed toes that splayed but not asfully as normal or motor block or anesthesia effect 1 animals.

Necropsy and Histology

Animals were sacrificed two weeks after implantation. Sections ofsciatic nerve approximately 2-3 cm in length, adjacent and proximal tothe implants, were preserved in 10% formalin solution (24 mM sodiumphosphate, pH 7). Sections were then embedded in paraffin, stained withhematoxylin and eosin, and examined by light microscopy.

Plasma Analysis

Rats (250-275 g) anesthetized with ketamine-HCl (100 mg/ml at 1.5 ml/kg,i.p.) and xylazine (4 mg/ml at 4 mg/kg, i.p.), were implanted with asilastic catheter into the right jugular vein. Blood was withdrawn (0.5cc) before implantation and at timed intervals after administration viathe indwelling central venous cannulae. Plasma was extracted with anequal volume of HPLC grade methanol (Fischer Scientific, Pittsburgh,Pa.), centriftiged (10,000×g) and the methanol phase filtered (0.2 μmnylon syringe type, Rainin, Woburn, Mass.) prior to HPLC analysis. TheHPLC reliably quantified bupivacaine concentrations in the plasmamethanol extraction phase down to 10 ng/ml. The bupivacaine standardsused for blood plasma analyses were added to plasma aliquots prior tomethanol extraction. The peak matching the standard bupivacaine peak'sretention time was verified in plasma samples by doping withbupivacaine.

Statistics

Data were analyzed using linear regression tests, ANOVA, Chi Squaretests and Wilcoxon rank-sum tests, where appropriate.

Example 3

Administration of Microspheres in combination with Glucocorticoids insolution

Example 1 demonstrated that incorporation of 0.05% dexamethasone intoeither pellets or microspheres resulted in prolongation of block from50-60 hours when microspheres which contained 0.05% dexamethasone wereused versus 6-10 hours in the case of microspheres which contained nodexamethasone. To further understand the mechanism, a model system wasdeveloped whereby different additives: steroids, steroidalanti-inflammatories, and non-steroidal anti-inflammatories (NSAIDs),were placed in the injection fluid to determine if the block could beprolonged and to screen for block prolonging activity. In this modelsystem, the additives were placed into the injection fluid immediatelyprior to injection, and the microspheres used contained bupivacaine, butno dexamethasone. If the additive was a solid, it was dissolved inethanol and aliquots of concentrations which varied between 0.005 and.5% (weight of additive/weight of microspheres). If the additive was inliquid form, then the amount was added directly to the injection fluid.

The results demonstrated that the duration of sciatic blockade oranesthesia effect from bupivacaine-polyester microspheres was prolongedby incorporation of glucocorticoid into the microspheres, which isproportional to the strength of the glucocorticoid in the injectionfluid.

Materials and Methods

Formulation of PLGA Microspheres and Protocol for In Vitro ReleaseStudies

Formulation of Microspheres of 65:35 loaded with 75% bupivacaine with0.05% dexamethasone

50 mg of PLGA 65:35 (High molecular weight) and 150 mg of bupivacainefree base (obtained from Perdue-Frederick) were dissolved in 0.1 ml of asolution of 5 mg of dexamethasone in 5 mIs in CH₂CL₂ and 0.9 mls ofCH₂CL₂. 1 ml of 0.3% polyvinyl alcohol (PVA) in 100 mM Tris buffer at.pH 8.5 was added. and the mixture vortexed 3 times for 15 seconds eachtime. The mixture was poured into 100 mls of 0.1% PVA in 100 mM Trisbuffer. The microspheres were examined using the light microscope andthe size distribution was determined, using a coulter counter, to bebetween 10 and 110 microns. The CH₂Cl₂ was removed by heating the sampleto 31° C. using a rotary evaporator at full vacuum for 15 minutes. Thesuspension of microspheres in 0.1% PVA was filtered through 140, 60, and20μ metal sleeves (Newark Wire Cloth Co.). Then the microspheres werefrozen in liquid nitrogen and lyophilized overnight.

Formulation of Microspheres which contained tritium labeleddexamethasone

Radiolabeled dexamethasone was purchased from Amersham and an aliquotwhich contained 200,000 counts was added to cold dexamethasone and themicrospheres were formulated as above.

Formulation of Microspheres which contained tritium labeled Bupivacaine

Radiolabeled bupivacaine was kindly donated by Dr. Gary Strichartz fromBrigham and Woman's Hospital. Again the bupivacaine was dissolved inethanol and an aliquot which contained 200,000 counts was added to coldbupivacaine and the microspheres were formulated as above.

Analysis of the in vitro release of either tritium labeled dexamethasoneor bupivacaine

The in vitro release studies were carried out as outlined above exceptthat instead of monitoring the release by U.V. spectroscopy, the invitro release was determined by adding 15 mls of Ecolume™ to each 2 mlaliquot of buffer, and the subsequent disintegrations were monitoredusing a scintillation counter.

Preparation of the Suspension

A ratio of 150 mg bupivacaine/kg was injected. The corresponding amountof microspheres is 200 mg/kg. The microspheres are weighed out andtransferred to a 3 cc syringe via the plunger. The needle of the syringeis removed and the opening covered with Parafilmm.Carboxymethylcellulose sterilized by filtration through a 0.2 micronfilter is used as the injection fluid.

The rats are tested at 0.5, 1, 2, 3, 6, 8 and 24 hours after injectionand then once daily until the block wears off. The rat is motor andsensory tested each time as described above using a hotplate at 56° C.

Results

Table 1 summarizes the results of these experiments.

TABLE 1 Sensory block Motor block Number of rats Additives (mg/Kg rat)(hours) (hours) 11 — 6.0 ± 1.0  5.0 ± 0.3 7  Dexamethasone (0.14) 47.0 ±8.0  38.0 ± 5.0 5  Dexamethasone (0.02) 17.0 ± 11.0 19.0 ± 8.0 5Dexamethasone (2.0) 36.0 ± 19.0  34.0 ± 12.0 5 Betamethasone (2.0)  44.0± 13.0  39.0 ± 11.0 5 Betamethasone (0.8)  46.0 ± 7.0  39.0 ± 5.0 5Betamethasone (0.25) 36.0 ± 10.0  38.0 ± 11.0 5  Betamethasone (0.032)19.0 ± 4.0  15.0 ± 4.0 5 Methylprednisolone (20)  34.0 ± 11.0 33.0 ± 9.07 Methylprednisolone (2.1) 28.0 ± 6.0  28.0 ± 5.0 5 Methylprednisolone(0.1) 20.0 ± 5.0  13.0 ± 4.0 7  Hydrocortisone (0.1) 10.0 ± 3.0  10.0 ±3.0 5   Hydrocortisone (1.25) 15.0 ± 5.0  16.0 ± 3.0 5 Hydrocortisone(10) 36.0 ± 10.0 31.0 ± 8.0 5 Ketoralac (2.0) 6.0 ± 0.7  7.0 ± 0.4 5Ketoralac (6.3) 8.0 ± 2.0 10.0 ± 4.0 4 Estradiol (1.25)  8.0 ± 1.0  9.0± 2.0 4 Estradiol (0.125) 11.0 ± 6.0  12.0 ± 6.0 8 Cholesterol (0.1) 4.0± 0.4  4.0 ± 1.0 5 Cholesterol (3.1) 8.0 ± 3.0  5.0 ± 1.0 5 Testosterone(1.7) 15.0 ± 5.0  15.0 ± 5.0 5 Testosterone (1.0) 7.0 ± 2.0  6.0 ± 1.0 4Progesterone (2.0) 8.0 ± 1.0  6.0 ± 1.0 5 Epinephrine (0.01) 12.0 ± 6.0 12.0 ± 4.0 5 Epinephrine (0.1)  14.0 ± 5.0  11.0 ± 3.0

The results demonstrate that dexamethasone does not produce sciaticblockade or anesthesia effect by itself in solution, nor does it prolongblockade or anesthesia effect from bupivacaine in solution. Addition ofdexamethasone in solution with bupivacaine in solution did not prolongblockade or anesthesia effect relative to bupivacaine in solution alone.The prolonged blockade or anesthesia effect previously observed seemedto require the presence of bupivacaine in microspheres.

A model system was developed in which dexamethasone was dissolved inethanol and an aliquot of known concentration was added to thesuspending medium which contained microspheres loaded with 75%bupivacaine. Addition of dexamethasone to the suspending medium inconcentrations ranging from 0.05% to 0.5% prolonged the duration ofblockade or anesthesia effect obtained using bupivacaine microspheres,Addition of 0.005% w/w bupivacaine did not result in a prolongation ofthe blockade or anesthesia effect obtained. The result of this modelsystem was useful, because it permitted testing of a series of compoundsover full concentration ranges for prolongation of sciatic block in vivowithout the labor-intensive step of making a microsphere prep with eachadditive and each dose.

Studies were conducted to determine whether dexamethasone's prolongationof blockade or anesthesia effect is unique, or whether it can bereplicated by: (1) other glucocorticoids, (2) other classes of steroids,or (3) other drugs with anti-inflammatory activity, includingnon-steroidals (NSAIDs). For example, it is well known that cholesteroland other steroids modify membrane lipid phase equilibria, and it isconceivable that effects on lipid physical state could perturb sodiumchannel function and amplify or prolong channel blockade from localanesthetics. The question was also raised as to whether thedexamethasone effect was due to changes in regional perfusion, analogousto epinephrine's effect.

FIG. 6 compares the effect of various glucocorticoids on duration ofnerve blockade or anesthesia effect when administered in combinationwith microspheres having bupivacaine incorporated therein. The dataconfirm that glucocorticoids prolong nerve block in proportion to theirpotentcy as glucocorticoids. It can be seen that:

1. High potency glucocorticoids such as betamethasone also produceprolongation of anesthesia up to 45 hours in duration.

2. Intermediate potency glucocorticoids such as methylprednisoloneproduce intermediate degrees of anesthetic prolongation.

3. Weaker glucocorticoids such as hydrocortisone produce mild, butstatistically significant prolongation of anesthesia.

4. The weaker prolongation of block by hydrocortisone cannot be made aseffective as dexamethasone by further increasing its concentration inthe suspending medium.

5. Estradiols showed little if any significant anesthesia-prolongingeffect under these conditions. Testosterone indicated a modestprolongation of anesthesia.

6. NSAIDs and epinephrine did not substantially prolong blockade oranesthesia effect, Epinephrine in the doses used (0.05% in thesuspending medium) produced considerable systemic toxicity, but nodeaths.

Preliminary reports on the histologic effects are that they are benign,with no evidence of major axonal or demyelinating injury and only mildinflammation.

A long duration of block was produced using 150 mg/kg rat body weightwith 75% bupivacaine loaded PLGA 65:35 microspheres. Doses as high as600 mg/kg can be given with temporary somnolence as a side-effect, butno convulsions or cardiac arrests.

The dosing of dexamethasone in the microspheres (0.05%) is quite low,particularly considering its delayed release. Even when thisconcentration of dexamethasone was added in the suspending medium(permitting immediate access for absorption), no systemic effects werefound. In one experiment using dexamethasone 0.5% in the suspendingmedium, no immediate toxicities occurred, but among five rats there weretwo deaths at 12-15 days post injection, and at the same time a thirdrat appeared thin and pale.

Experiments confirmed that 65:35 PLGA polymers were preferable to either75:25 PLGA or 100% PLA, both in terms of (1) the reliability, intensityand duration of sciatic nerve block, (2) each of dispersal andinjectability. A blockade or anesthesia effect of 30-40 hours wasobserved with PLGA 50:50 over the PLGA 65:35 microspheres, indicating noadvantage.

Example 4

The combination of local anesthetic in microspheres with glucocorticoidis not a result of altered release rates in vivo

Additional studies were conducted as described above to furtherelucidate the mechanisms involved in the prolongation of the nerveblockade or anesthesia effect by the glucocorticoid. In this study,bupivacaine (measured in mg) remaining in. microspheres that wereextracted from rats as a function of time in days following injectionwas determined (data not shown). The study compared the amount ofbupivacaine released as a function of polymer, comparing PLGA 75:25 withand without dexamethasone, PLGA 65:35 with and without dexamethasone,PLGA 50:50 with and without dexamethasone, and PLA containingbupivacaine and dexamethasone. The results demonstrate that the drug isbeing released over time as expected, and that release is not altered bythe presence or absence of dexamethasone. Accordingly, while not wishingto be bound by any hypothesis as to how this occurs, the glucocorticoidmay be exerting an effect directly on the nerve, not by interaction withthe local anesthetic.

The examples provided above are not meant to be exclusive. Many othervariations of the present invention would be obvious to those skilled inthe art, and are contemplated to be within the scope of the appendedclaims. Numerous publications are cited herein, the disclosures of whichare incorporated herein by reference in their entireties.

What is claimed is:
 1. A formulation for providing pain relief at a sitein a patient comprising a local anesthetic in a biocompatiblebiodegradable controlled release form and a glucocorticosteroid in anamount effective to prolong the effect of the local anesthetic such thatthe duration of effect is greater than that obtained by use of the samedose of local anesthetic in controlled release form in the absence ofthe glucocorticosteroid.
 2. The formulation of claim 1 wherein thecontrolled release form comprises a biocompatible polymer.
 3. Theformulation of claim 1 wherein at least a portion of theglucocorticosteroid is incorporated into a separate controlled releaseform.
 4. The formulation of claim 2 wherein the polymer is selected thegroup consisting of polyanhydrides, copolymers of lactic acid andglycolic acid, polyorthoesters, proteins, and polysaccharides.
 5. Theformulation of claim 2 wherein the polymer is a copolymer of lactic acidand glycolic acid.
 6. The formulation of claim 5 wherein the copolymercomprises a ratio of lactic acid and glycolic acid ranging from about75:25 to about 50:50 by weight.
 7. The formulation of claim 1 whereinthe glucocorticosteroid is selected from the group consisting ofdexamethasone, cortisone, prednisone, hydrocortisone, beclomethasonedipropionate, betamethasone, flunisolide, methylprednisone,paramethasone, prednisolone, triamcinolone, alclometasone, amcinonide,clobetasol, fludrocortisone, diflorasone diacetate, fluocinoloneacetonide, fluocinonide, fluorometholone, flurandrenolide, halcinonide,medrysone and mometasone and pharmaceutically acceptable mixtures andsalts thereof.
 8. The formulation of claim 1 wherein theglucocorticosteroid is incorporated at a loading between about 0.001 andabout 30 percent by weight.
 9. The formulation of claim 1 wherein theglucocorticosteroid is dexamethasone.
 10. The formulation of claim 1wherein the local anesthetic is in free base form.
 11. The formulationof claim 1 wherein the local anesthetic is selected from the groupconsisting of bupivacaine, ropivacaine, dibucaine, procaine,chloroprocaine, prilocaine, mepivacaine, etidocaine, tetracaine,lidocaine, and xylocaine, and mixtures thereof.
 12. The formulation ofclaim 1 wherein the local anesthetic is incorporated into the controlledrelease form at a percent loading of ranging from about 60% to about 85%by weight.
 13. The formulation of claim 1 which is in the form selectedfrom the group consisting of slabs, beads, pellets, microparticles,microspheres, microcapsules, and pastes.
 14. The formulation of claim 13which comprises a plurality of microparticles.
 15. The formulation ofclaim 14, which comprises microspheres. suspended in a pharmaceuticallyacceptable carrier for administration by a method selected from thegroup consisting of injection, infiltration, infusion or topicalapplication.
 16. The formulation of claim 15 wherein at least a portionof the glucocorticosteroid is present in said pharmaceuticallyacceptable vehicle for injection.
 17. The formulation of claim 15further comprising an outer coating wherein the outer coating fliercomprises a pharmaceutically active agent for immediate release selectedfrom the group consisting of a glucocorticosteroid and a localanesthetic and mixtures thereof.
 18. The formulation of claim 1 whereinthe local anesthesia is effective from about 0.1 hour to about 200 hoursafter administration.
 19. The formulation of claim 1 wherein the localanesthesia is effective from about 1 hour to about 150 hours afteradministration.
 20. A formulation for sustained release of a localanesthetic at a site in a patient comprising a local anesthetic and aglucocorticosteroid incorporated into a biocompatible biodegradablepolymer, the formulation including the local anesthetic in aconcentration effective to provide pain relief at the site and theglucocorticosteroid in a concentration effective to prolong the effectof the local anesthetic such that the duration of effect is greater thanthat obtained by use of the same dose of local anesthetic in controlledrelease form in the absence of the glucocorticosteroid.
 21. A method forproviding pain relief at a site in a patient, comprising administering alocal anesthetic in a controlled release form and administering aglucocorticosteroid at the site in an amount effective to substantiallyprolong the effect of the local anesthetic such that the duration ofeffect is greater than that obtained by use of the same dose of localanesthetic in controlled release form in the absence of theglucocorticosteroid.
 22. The method of claim 21 wherein the controlledrelease form comprises a biocompatible polymer.
 23. The method of claim22 wherein the polymer is selected from the group consisting ofpolyanhydrides, copolymers of lactic acid and glycolic acid,polyorthoesters, proteins, and polysaccharides.
 24. The method of claim21 wherein at least a portion of the glucocorticosteroid is incorporatedinto a separate biocompatible polymer from the local anesthetic.
 25. Themethod of claim 21 wherein the glucocorticosteroid is selected from thegroup consisting of dexamethasone, cortisone, prednisone,hydrocortisone, beclomethasone dipropionate, betamethasone, flunisolide,methylprednisone, paramethasone, prednisolone, triamcinolone,alclometasone, amcinonide, clobetasol, fludrocortisone, diflorasonediacetate, fluocinolone acetonide, fluocinonide, fluorometholone,flurandrenolide, halcinonide, medrysone and mometasone andpharmaceutically acceptable mixtures and salts thereof.
 26. The methodof claim 21 wherein the glucocorticosteroid is dexamethasone.
 27. Themethod of claim 21 wherein the local anesthetic is in free base form.28. The method of claim 21 wherein; the local anesthetic is selectedfrom the group consisting of bupivacaine, ropivacaine, dibucaine,procaine, chloroprocaine, prilocaine, mepivacaine, etidocaine,tetracaine, lidocaine, and xylocaine, and mixtures thereof.
 29. Themethod of claim 21 wherein the anesthetic is incorporated into thepolymer at a percent loading ranging from about 60 percent to about 90percent by weight.
 30. The method of claim 21 wherein the formulation isin the form selected from the group consisting of slabs, beads, pellets,microparticles, microspheres, microcapsules, and pastes.
 31. The methodof claim 30 wherein the formulation comprises a plurality ofmicroparticles.
 32. A formulation for sustained release of a localanesthetic according to claim 1, wherein the controlled release formcomprises microcapsules comprising the local anesthetic, theglucocorticosteroid, and a biocompatible, biodegradable polymer, whereinthe local anesthetic is present in said microcapsules at a weightpercent ranging from about 70 to about 90%.
 33. A formulation forproviding prolonged pain relief at a site in a patient comprising alocal anesthetic incorporated into a biocompatible, biodegradablecontrolled release form selected from the group consisting of slabs,beads, pellets, microparticles, microspheres, microcapsules, and pastes,said local anesthetic being contained in said controlled release form ata percent loading ranging from about 60 percent to about 90 percent byweight, said controlled release form further comprising aglucocorticosteroid in an amount effective to prolong the effect oflocal anesthetic such that the duration of effect is greater than thatobtained by use of the same dose of local anesthetic in controlledrelease form in the absence of the glucocorticosteroid.
 34. Theformulation of claim 33 which comprises microcapsules.
 35. Theformulation of claim 34, which comprises microcapsules or microspheressuspended in a pharmaceutically acceptable carrier for administration bya method selected from the group consisting of injection, infiltration,infusion or topical application.
 36. The formulation of claim 33 whereinthe biocompatible, biodegradable controlled release form comprises apolymer selected from the group consisting of polyanhydrides, copolymersof lactic acid and glycolic acid, polyorthoesters, proteins, andpolysaccharides.
 37. The formulation of claim 36, wherein thebiocompatible, biodegradable controlled release form comprises acopolymer of lactic acid and glycolic acid.
 38. The formulation of claim37, wherein the copolymer comprises a ratio of lactic acid and glycolicacid ranging from about 75:25 to about 50:50 by weight.